1. Field of the Invention
The present invention relates to lubricating electrical contact pads located along the edges of printed circuit cards. More specifically it relates to automatically and reliably applying uniform amounts of liquid lubricant to gold electrical contact tabs.
2. Description of the Prior Art
In the computer industry, there is frequently a need to replace printed circuit cards during the life of a machine. Galling and brittle fracture of noble plating material occurs when contact force per unit area exceeds the strength of the substrate metal. Failure of a connector through increased resistance can be caused by excessive wear resulting from friction of mating parts and may also cause interference with operation of the connector. Excessive wear is detrimental from an electrical as well as mechanical view point.
It is known that a lubricant can have beneficial electrical as well as mechanical effects. A lubricant when applied to separable contacts as a thin film reduces friction and wear during sliding action of contacting surfaces. Wear reduction is particularly important where thin precious metal plating is used over base metal.
A method for use in a manufacturing process for applying a thin, uniform layer of lubricant on gold contact tabs is desirable. Conventional methods include felt tips with lubricant, cotton swabs with lubricant, and wiping on lubricant with a lint free cloth. The main drawback of these methods is that the amount of lubricant on contact tabs is not consistent due to the manual nature of the methods.
Therefore, it is desirable to assure that card contact edges are lubricated at the time of manufacture with a sufficient amount of lubricant to enable specified insertions and retractions of such cards during their useful life. In some instances this lifetime may be expected to last for up to five years and include as many as 25 insertions/retractions. It has been found that liquid lubricants are most effective for providing lifetime lubrication at the time the cards are manufactured. However, the problem of assuring uniform application of lubricant has not been solved with total success; and in fact is often a manual step -- with its inherent deficiencies in repeatability and reliability.
Other methods of lubricating printed circuitry have included applying a layer of spray wax and using rollers such as taught in U.S. Pat. No. 4,159,222 to Lebow et al. U.S. Pat. No. 4,268,568 to Sard et al describes electrical contacts on printed circuit boards, which contacts incorporates a fluorocarbon polymer film as a lubricant. U.S. Pat. Nos. 4,529,531 and 4,530,772 to Padovani and Timony, respectively, disclose electric contact lubricants and methods of using them. In each case the method comprises adding the disclosed lubricant to the contacts.
In an automated production environment, it is desirable for the lubrication process to perform several functions including supplying a continuous lubricant film in controlled amounts while moving a card past the supply point at a controllable speed, while accommodating card thickness variations.